INFLUENCE OF SLAG SAND AND FLY ASH AGGREGATE ON THE FRESH AND STRENGTH PROPERTIES OF SELF-COMPACTING CONCRETE

Abstract

This study investigates the combined influence of slag sand as fine aggregate and fly ash aggregate as partial coarse aggregate replacement on the fresh and strength behavior of Self-Compacting Concrete (SCC). Six mixes were developed by varying slag sand from 0% to 100% in increments of 20%, while maintaining a constant 40% replacement of natural coarse aggregate with fly ash aggregate. Fresh concrete performance was assessed through slump flow, T50 time, V-funnel, U-box, and L-box tests in accordance with EFNARC guidelines. Results showed a steady improvement in flowability, reduced viscosity, and enhanced passing ability with increasing slag sand content, with Mix A6 exhibiting the highest slump flow (612 mm) and the lowest T50 time (4.60 s). Mechanical properties were evaluated at 7, 28, and 90 days. The highest 28-day compressive strength (42.91 MPa) and split tensile strength (4.68 MPa) were recorded for Mix A2, corresponding to a 20% slag sand replacement. The initial rise in strength is attributed to improved packing density, reduced surface roughness, and better particle morphology associated with slag sand, which enhances interfacial transition zone quality. Further increase in slag sand content beyond 20% resulted in a gradual reduction in strength due to higher fineness and potential water demand effects. The study demonstrates that the combined use of slag sand and fly ash aggregate can produce SCC with excellent flow characteristics and satisfactory strength performance, offering a sustainable alternative to natural aggregates. Mix A2 is identified as the optimum composition for balancing fresh and mechanical properties.